The present invention relates to an apparatus for directly coupling an analytical column used in a liquid chromatograph (herein after called LC) or a flow injection analysis device (herein after called FIA) with a mass spectrometer (herein after called MS), and more particularly to an apparatus for successively trapping a component of interest in a trapping column, washing (desalting) the trapped component of interest, eluting the trapped component of interest and washing the trapping column so as to transmit an eluate from the trapping column to MS.
In the conventional LC/MS apparatus, the trapping, the washing(desalting), the eluting and the washing processes are performed as shown in FIG. 24.
That is, liquid sample is injected in solution of a mobile phase A through an injection port by using a micro-syringe and is separated according to components of the sample by analytical column 4.
Then, an eluate A eluted from the analytical column 4 is diluted with solution of mobile phase B and is transmitted to a trapping column TC, whereby a component of interest for analysis in the eluate is trapped by the column TC and others in the eluate are wasted to a drain DR.
After that, as shown in a central position of FIG. 24, only the solution of mobile phase B such as water, flows in the column TC so as to wash, that is, desalt the column TC and eluate D from the column TC are wasted to the drain DR.
Then, as shown in a right-hand side of FIG. 24, solution of the mobile phase C such as organic solvent etc. flows in the column TC, whereby the components of interest trapped in the column TC are successively eluted as eluate C and are transmitted to the mass spectrometer so as to analyze mass of the components.
Meanings of the words frequently used hereinafter will be explained as shown in a following table.
______________________________________ Words Meanings ______________________________________ solution of the eluent for being analyzed by LC mobile phase A eluate A eluate eluted from the analytical column 4 solution of the diluent for diluting the eluate mobile phase B A, and washing (desalting) liquid for the trapping column TC confluenced eluate mixed solution of the eluate A and the mobile phases B eluate B the confluenced eluate eluted from the TC eluate D the solution of the mobile phase B eluted from the TC after washing (desalting) solution of the eluent for eluting the mobile phase C components of interest trapped in the TC eluate C eluate containing the components of interest eluted from the TC ______________________________________
Sample solutions analyzed by the LC or FIA generally contain nonvolatile ionic substances, and solutions containing nonvolatile salt and buffer substances are widely used as the solution of the mobile phase A.
When such nonvolatile substances are used solely in LC or FIA, few problems arise.
In the case of an LC/MS, the LC/MS may be used to sample gas, liquid, ions etc., which must pass through a small aperture or a capillary tube into a high vacuum region. In such a situation, the nonvolatile substances may be deposited around the small aperture or inside of the capillary tube, so that deposits clog them. Therefore, this problem has prevented the use of mobile phases containing nonvolatile substances in LC/MS apparatuses.
The Japanese laid-open Patents Nos. 3-175355(1991), 62-138753(1987) and 62-19758(1987) show an apparatus which traps component of analyte in a trapping column, the components of interest are washed (desalted) with solution of the mobile phase B, and the components of interest are eluted with a solution of the mobile phase C in order to solve the above problem.
FIG. 3 shows a block diagram of a conventional system for washing, desalting, trapping and eluting the components of interest as shown in the above Japanese laid-open Patent.
Numeral 1 shows a solvent of the mobile phase A containing the nonvolatile buffer which is transmitted by a pump 2, and a sample solution is injected through a sample injection port 3 by a micro-syringe. The sample solution is separated according to the components thereof in a analytical column by the solvent of the mobile phase A so as to successively elute from the analytical column and to be detected by a detector 5.
Then, eluate A from the analytical column 4 is desalted by a desalting system 60. Desalting process in the desalting system 60 is performed by changing the flow path using a plurality of valves.
At first, after trapping the components of interest in a trapping column 61, the components of interest are washed, that is, are desalted with the solution of the mobile phase B such as water. Then, the component of analyte is eluted by the solution of mobile phase C which does not contain nonvolatile substance and is transmitted to a mass spectrometer 8 or a fraction collector.
In the system shown in FIG. 3, there is a problem as that the component being desalted may be analyzed, but other components contained in the sample are wasted to the drain DR and are not analyzed.
Further, FIG. 4 shows a system having a plurality of trapping columns TC1, TC2, TC3 which are used by successively collecting eluate from analytical column 4. This is accomplished by exchanging trapping columns by change-over valves 62, 63 in order to analyze multiple successive components of interest.
That is, the trapping columns TC1, TC2, TC3 are changed over when the components of interest eluted from a analytical column 4 are detected and thereby successively trapping the components of interest. After every column finishes trapping the components, the valves 62, 63 are changed over again, and the trapped components of interest are desalted, then eluted by the solution of the mobile phase C and transmitted to a mass spectrometer 8 or a fraction collector.
Further, a system using only one trapping column with a plurality of sampling loops was proposed.
In the conventional system as shown in FIG. 3, the component of analyte trapped in the trapping column is desalted and eluted when measuring the sample solution with LC, and therefore, it is needed for the trapping columns to be pretreated before every measurement of the liquid sample.
In order to analyze one objective component, it takes a time T as follows;
T={measuring time by LC+desalting and eluting time+analyzing time by the MS+pretreating time of TC}
Therefore, it takes so much time for analysis that it is difficult to perform it quickly and automatically.
Further, in order to analyze one component of interest in the conventional system as shown in FIG. 4, it takes a time T as follows;
T={measuring time by LC+desalting and eluting time+analyzing time by the MS+(pretreating time of TC) (number of components of interest trapped in TC)}
Therefore, more time for analysis is needed when the number of the components of interest is more than number of the TC. The analysis by the LC as above is performed by using the solution of the mobile phase A for nonvolatile substance, but the system becomes more complicated and more expensive in the following cases;
(1) The solution of mobile phase used for the analysis contains volatile substances. PA1 (2) An analysis means is used which does not need separation by analytical column. PA1 (3) The MS needs a means for preventing an introduction of the components of non-interest. PA1 (a) At least one fixed member and a movable member which is rotated with respect to an axis and is slidable to and connected to a fixed member. PA1 (b) The fixed member has at least four output holes therein. PA1 (c) The movable member has four tubes around the axis and mounts at least four trapping columns respectively connected to the tubes, thereby the tubes are slidable and change over the holes so as to successively connect to the tubes. PA1 (d) The four output holes are respectively connected to the trapping columns so as to perform four processes in parallel as follows; PA1 (1) first analytical mode for washing the trapping column and introducing eluate from the analytical column to the mass spectrometer, PA1 (2) second analytical mode for trapping a component of interest contained in eluate eluted from the analytical column by the trapping columns and washing the mass spectrometer, PA1 (3) third analytical mode for eluting the component of interest trapped in the trapping columns and introducing the component of interest to the mass spectrometer, and PA1 (4) fourth analytical mode for washing the trapping columns and the mass spectrometer, and for draining the eluate from analytical column.